This invention will be described using a warp knitting machine as an example, though knitting machines include a warp-, flat- and circular knitting machine and the like, and similarly it can be applied to such a weft or circular machine.
The warp knitting machine is roughly classified into tricot and raschel machines, on which a sectional beam wound with knitting yarn or warp end is usually mounted, the warp end being supplied therefrom to a knitting needle line to perform knitting.
The knitting parts (tool) consisting of a knitting section of a warp knitting machine comprises a thin sheet formed "guide" of about 200 .mu.m thick which is located between a sectional beam and a knitting needle line and has a hole to guide knitting yarn or warp end, a thin sheet-formed "needle" with a hook on a head end for knitted stitch formation, and a thin sheet-formed "tongue", which cooperatively participates in the knitted stitch formation together with the needle, and "sinker", as well as "separator", "jacquard guide needle", etc., in general, a number of such parts being arranged parallel at very close spaces to form a block.
Generally, from viewpoints of easy processing and wear resistance, a carbon steel base material shaped to profile each of these parts is coated by means of wet chromium plating and used as various knitting parts described above.
The durability of such knitting parts, however, has been in serious question due to speeding up of knitting machines, diversification of materials for knitting yarn such as high strength fibers or modified fibers and employment of various kinds of sizes.
Namely, the knitting parts such as guide, needle, tongue, sinker, separator, jacquard guide needle, etc. tend to be worn out at a portion contacting with knitting yarn, which would cause hairiness or end breakage of the yarn, and thus the durability of such parts is an important factor to decide the operational effectiveness of machines and the cost of products because it requires a great deal of expense, effort and time to replace a great number of these parts used in a machine so as to prevent such a trouble of the yarn described above.
Then, it has been proposed to coat the surface of knitting parts (tool) for warp knitting machines with high hardness coating of metals such as tantalum (Ta), tungsten (W), titanium nitride (TiN), titanium-tungsten alloy (TiW), etc. (see Japanese Patent Laid-Open Publication No. 4-41,755).
It has also been known, however, that wearing of knitting parts typically represented by the guide is a phenomenon difficulty caused by kinds of fibers, impact pressure, vibration characteristics, etc., and that satisfied results are not necessarily obtained by a coating of high surface hardness.
In fact, in the case of a guide coated with titanium nitride which is known as a coating of a high hardness compound, no increase in durability was observed, compared with conventional one coated by means of chromium plating, and aroused a problem that the substrate was softened due to a higher treating temperature.
Further, it is also reported that the toughness of a base material itself is lost and, as a result, the durability is decreased on the contrary when a coating of high hardness is thickly formed on the base material. From this point of view, it is necessary to improve the durability without spoiling inherent properties of the substrate.
Accordingly, this invention has been accomplished in consideration of such a technical background described above, and it is an object of this invention to greatly improve the durability of knitting parts so as to be widely suited to various yarn made of a variety of materials including from natural fibers to high strength synthetic fibers, thereby the operational effectiveness of knitting machines and the cost of products being increased and decreased, respectively.